Temperature Measurement Using Infrared Spectral Band Emissions From H₂O

Currently, there is no satisfactory method for measuring the temperature of the gas phase of combustion products within a solid fuel flame. The industry standard, a suction pyrometer or aspirated thermocouple, is intrusive, spatially and temporally averaging, and difficult to use. In this work, a new method utilizing the spectral emission from water vapor is investigated through modeling and experimental measurements. The method employs the collection of infrared emission from water vapor over discrete wavelength bands and then uses the ratio of those emissions to infer temperature. This method was demonstrated in the products of a 150 kWth natural gas flame along a 0.75 m line of sight, averaged over 1 min. Results from this optical method were compared to those obtained using a suction pyrometer. Data were obtained at three fuel air equivalence ratios that produced products at three temperatures. The optical measurement produced gas temperatures approximately 3–4% higher than the suction pyrometer. The uncertainty of the optical measurements is dependent on the gas temperature being ±9% at 850 K and 4% or less above 1200 K. Broadband background emission assumed to be emitted from the reactor wall was also seen by the optical measurement and had to be removed before an accurate temperature could be measured. This complicated the gas measurement but also provides the means whereby both gas and solid emission can be measured simultaneously.